required for the understanding of the drawings, a single word or words such as “water”, “steam”, “open”, “closed”, “section AA” and in the case of electric circuits and block schematic or flowsheet diagrams, a few short catchwords; and (n) flow sheets and diagrams are considered drawings for the purposes of these Regulations. 22. Abstracts. (1) The abstract shall consist of the following— (a) a summary of the disclosures contained in the description, the claims and any other drawings indicating the technical field to which the invention pertains and drafted in a way which allows the clear understanding of the technical problem, the gist of the solution of that problem through the invention and the principal use or user of the invention; and (b) where applicable, the chemical formula which, among all the formulae contained in the application, best characterises the invention. (2) The abstract shall be so drafted that it can efficiently serve as a scanning tool for purposes of searching in the particular art. (3) The abstract shall be as concise as the disclosure permits and shall, whenever practicable, consist of not less than 50 but not more than 150 words. (4) The abstract shall not contain statements on the alleged merits or value of the invention. (5) Each main technical feature mentioned in the abstract and illustrated by a drawing in the application shall be followed by a reference sign placed between parentheses. (6) The abstract shall be accompanied by the most illustrative of any drawings furnished by the applicant. 23. Declaration of priority. (1) The application may contain a declaration claiming priority as provided for in the Paris Convention, of one or more earlier national, regional